With the recent increase in the amount of communication and information, wireless communication technology using a high-frequency band capable of transmitting a large amount of information at high speed has been attracting attention. Particularly in 60 GHz band, each transmitter can use the band of 2.5 GHz without a license. Accordingly, the use of such a radio enables communication at a speed of 1 Gbps or higher.
However, electromagnetic waves in a high-frequency band have strong directivity, which makes it difficult to establish a communication using diffracted electromagnetic waves. Therefore, if there is a shielding such as a person suddenly appearing between wireless communication apparatuses, a problem occurs in which the communication is interrupted. In such wireless communication apparatuses (wireless transmitter and receiver) using electromagnetic waves in a high-frequency band, when the communication therebetween is interrupted, it is necessary to control an antenna radiation pattern of each wireless communication apparatus to search the strongest electromagnetic wave among electromagnetic waves reflected at walls of a building or a house, and to establish a communication using a path which is a propagation channel of this electromagnetic wave.
As one method to control the radiation pattern of an electromagnetic wave output from a transmitter of a wireless communication apparatus, a method using a so-called array antenna is known. Specifically, in the method, the radiation pattern is changed by controlling a phase of a signal transmitted from each antenna element. The term “array antenna” herein described refers to an antenna in which a plurality of antenna elements are arranged in an array.
As disclosed in Non Patent Literature 1, for example, there is a method of adding phase information to a local signal output from a local oscillator by use of a phase shifter for processing a signal in a high-frequency band, in order to control a phase of a signal transmitted from an antenna. However, the phase shifter for a high-frequency band has a great loss, and thus a new amplifier is required so as to compensate for the loss. This causes a problem of an increase in circuit size and further an increase in power consumption.
In Patent Literature 1, which is the prior application of the present application, the applicant of the present application has proposed a method of configuring a phase shifter for a baseband signal band, and adding phase information about a signal transmitted from an antenna to baseband signals, without using a phase shifter for a high-frequency band having a great loss.